----- Original Message ----- From: "Scott Loveless" Subject: Flash bulbs (or, blast from the past)
> Lately, I've had an opportunity to look at some Kodachrome exposed with > M2B blue flash bulbs. The character of the light is certainly different > than that of electronic flash. A couple dozen of these could be in my > very near future. > > And now, of course, my dilemma. I'm hoping that a few of you have some > experience with flash bulbs and can shed some, er, light on the > situation. The chart here http://www.flashbulbs.com/bluebulb.htm > suggests that these bulbs will X sync to 1/30. The manuals for the MX > and SP500 recommend 1/15 at the fastest, while the K1000 manual > recommends 1/30. This seems a bit odd to me. As this sort of > photography is relatively expensive, I'd rather not experiment too > much. (Kodachrome + processing + bulbs at $1per that may not fire) > > Does anyone recall how they may have used these bulbs? I'm guessing > that I'd be safe at 1/15, but if I can squeeze out 1/30 I'd be happy. > > Thanks a bunch, folks! Bob Shell will know more about this (he has probably forgotten a thousand times what I know) but I'll try. Unlike an electronic flash, a bulb flash is not instantaneous light. The bulb has a warm-up time of several milliseconds prior to it reaching full output. Some cameras have an X/M switch, X being for gas discharge flash units, M being for flash bulbs. The M setting triggers the flash well in advance of the shutter being fully open to allow the bulb to peak before the shutter opens fully. In the absence of a camera adjustment, the flash will be triggered when the leading curtain fully opens. If the shutter speed is set too fast, the trailing curtain will close before the bulb heats up fully, resulting in (partial frame) underexposure and poor colour balance. Some bulbs heat up faster than others, and allow a faster shutter speed off the X setting. This may not be accounted for in the camera owners manual, hence the difference in recommendations from the bulb manufacturer and camera documentation. For myself, I would follow the bulb manufacturers recommendation regarding shutter speed, though you won't go wrong slowing things down a stop either, providing ambient light levels will allow it. William Robb -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
